When oil or other flammable materials are stored in liquid form, as for example in well head production tanks, vapour from the oil or from gases entrapped with the oil often escapes the oil and may be released into the atmosphere from the storage tank where it can be easily ignited or cause an environmental danger due to its toxicity. It is therefore desirable to pump the vapour away from the oil storage area and burn it in a controlled manner at a flare stack.
The inventor has found that drawing vapour from the oil storage tank can create a dangerous condition by drawing air into the storage tank from the atmosphere. This occurs if, in pumping the vapour from the storage tank, a vacuum is created in the outlet line from the oil storage tank.
The inventor has therefore provided a device that places constant pressure on the storage tank while allowing vapour to be pumped out of the storage tank.
Therefore in one aspect of the invention, the inventor has provided a vapour transfer pump for a storage tank comprising:
an inlet line connected to the storage tank;
a first one way check valve on the inlet line;
an expandable container connected to the inlet line;
first means disposed about the expandable container and reciprocable independently of the expandable container for forcing vapour out of the expandable container;
second means to reciprocate the first means about the expandable container;
an outlet line connected to the expandable container and connectable to a flare stack; and
a second one way check valve on the outlet line.
In a preferred embodiment, the expandable container is a bladder, and the first means is formed from a stationary plate and a reciprocating plate, the bladder being disposed between the stationary plate and the reciprocating plate.